feat(calendars): add app-side enable/disable for calendars

Introduce a second, heavier visibility level above the per-view hide
filter. A disabled calendar is removed from the app's surfaces entirely —
its events drop out of all views and search, and it disappears from the
drawer filter list, the event-form calendar picker and the import target
picker. It stays listed only in Settings → Calendars, where a per-row
switch toggles it, so it can always be brought back.

- CalendarPrefs: disabledCalendarIds set + setter, mirroring the hidden
  set (DataStore comma-separated string); never touches the system
  VISIBLE/SYNC_EVENTS flags, so it's app-local and reversible.
- CalendarRepositoryImpl: instances()/searchEvents() exclude
  calendarId ∈ (hidden ∪ disabled). distinctUntilChanged() on instances
  collapses the transient duplicate emission both DataStore-derived sets
  produce when either is toggled.
- FilterViewModel: drop disabled calendars from the drawer filter list.
- EventEditViewModel: exclude disabled from writableCalendars; a
  last-used preselect on a now-disabled calendar falls back to the first
  remaining writable one.
- ImportViewModel: exclude disabled from the import target list.
- CalendarsScreen/ViewModel: per-row enable/disable Switch on both the
  local and synced groups; disabled rows render dimmed (new GroupedRow
  `dimmed` flag) while keeping the toggle live.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/test/java/de/jeanlucmakiola/calendula/data/calendar/CalendarRepositoryImplTest.kt

@@ -170,6 +170,74 @@ class CalendarRepositoryImplTest {
         }
     }
 
+    @Test
+    fun `instances drops events whose calendar the user disabled`(@TempDir tempDir: Path) = runTest {
+        val prefs = newPrefs(tempDir)
+        prefs.setDisabledCalendarIds(setOf(2L))
+        val fake = FakeCalendarDataSource().apply {
+            instancesResult = { _, _ ->
+                listOf(
+                    makeEvent(10L, "Enabled", calendarId = 1L),
+                    makeEvent(11L, "Disabled", calendarId = 2L),
+                )
+            }
+        }
+        val repo = CalendarRepositoryImpl(fake, prefs, newSettings(tempDir), UnconfinedTestDispatcher(testScheduler))
+
+        val range = Instant.fromEpochMilliseconds(0)..Instant.fromEpochMilliseconds(10_000L)
+        repo.instances(range).test {
+            assertThat(awaitItem().map { it.title }).containsExactly("Enabled")
+            cancelAndIgnoreRemainingEvents()
+        }
+    }
+
+    @Test
+    fun `instances applies the union of hidden and disabled sets`(@TempDir tempDir: Path) = runTest {
+        val prefs = newPrefs(tempDir)
+        prefs.setHiddenCalendarIds(setOf(2L))
+        prefs.setDisabledCalendarIds(setOf(3L))
+        val fake = FakeCalendarDataSource().apply {
+            instancesResult = { _, _ ->
+                listOf(
+                    makeEvent(10L, "Shown", calendarId = 1L),
+                    makeEvent(11L, "Hidden", calendarId = 2L),
+                    makeEvent(12L, "Disabled", calendarId = 3L),
+                )
+            }
+        }
+        val repo = CalendarRepositoryImpl(fake, prefs, newSettings(tempDir), UnconfinedTestDispatcher(testScheduler))
+
+        val range = Instant.fromEpochMilliseconds(0)..Instant.fromEpochMilliseconds(10_000L)
+        repo.instances(range).test {
+            assertThat(awaitItem().map { it.title }).containsExactly("Shown")
+            cancelAndIgnoreRemainingEvents()
+        }
+    }
+
+    @Test
+    fun `instances re-emits when the disabled set changes`(@TempDir tempDir: Path) = runTest {
+        val prefs = newPrefs(tempDir)
+        val fake = FakeCalendarDataSource().apply {
+            instancesResult = { _, _ ->
+                listOf(
+                    makeEvent(10L, "A", calendarId = 1L),
+                    makeEvent(11L, "B", calendarId = 2L),
+                )
+            }
+        }
+        val repo = CalendarRepositoryImpl(fake, prefs, newSettings(tempDir), UnconfinedTestDispatcher(testScheduler))
+
+        val range = Instant.fromEpochMilliseconds(0)..Instant.fromEpochMilliseconds(10_000L)
+        repo.instances(range).test {
+            assertThat(awaitItem().map { it.title }).containsExactly("A", "B").inOrder()
+
+            prefs.setDisabledCalendarIds(setOf(2L))
+
+            assertThat(awaitItem().map { it.title }).containsExactly("A")
+            cancelAndIgnoreRemainingEvents()
+        }
+    }
+
     @Test
     fun `createEvent delegates and returns the new id`(@TempDir tempDir: Path) = runTest {
         val fake = FakeCalendarDataSource().apply { nextInsertId = 77L }

app/src/test/java/de/jeanlucmakiola/calendula/data/prefs/CalendarPrefsTest.kt

@@ -50,4 +50,34 @@ class CalendarPrefsTest {
         }
         assertThat(prefs.hiddenCalendarIds.first()).isEqualTo(setOf(1L, 3L))
     }
+
+    @Test
+    fun `disabledCalendarIds defaults to empty when unset`(@TempDir tempDir: Path) = runTest {
+        val prefs = CalendarPrefs(newDataStore(tempDir))
+        assertThat(prefs.disabledCalendarIds.first()).isEmpty()
+    }
+
+    @Test
+    fun `setDisabledCalendarIds round-trips through DataStore`(@TempDir tempDir: Path) = runTest {
+        val prefs = CalendarPrefs(newDataStore(tempDir))
+        prefs.setDisabledCalendarIds(setOf(1L, 42L, 7L))
+        assertThat(prefs.disabledCalendarIds.first()).isEqualTo(setOf(1L, 42L, 7L))
+    }
+
+    @Test
+    fun `setting empty disabled set clears storage`(@TempDir tempDir: Path) = runTest {
+        val prefs = CalendarPrefs(newDataStore(tempDir))
+        prefs.setDisabledCalendarIds(setOf(1L))
+        prefs.setDisabledCalendarIds(emptySet())
+        assertThat(prefs.disabledCalendarIds.first()).isEmpty()
+    }
+
+    @Test
+    fun `hidden and disabled sets are stored independently`(@TempDir tempDir: Path) = runTest {
+        val prefs = CalendarPrefs(newDataStore(tempDir))
+        prefs.setHiddenCalendarIds(setOf(1L))
+        prefs.setDisabledCalendarIds(setOf(2L))
+        assertThat(prefs.hiddenCalendarIds.first()).isEqualTo(setOf(1L))
+        assertThat(prefs.disabledCalendarIds.first()).isEqualTo(setOf(2L))
+    }
 }